二代鎳基單晶高溫合金的顯徽結(jié)構(gòu)演變
發(fā)布時間：2018-07-23 19:26
【摘要】：鎳基單晶高溫合金是廣泛應用于航空發(fā)動機渦輪葉片的首選結(jié)構(gòu)材料,其工作特點是高溫和高應力環(huán)境。該類合金在高溫下仍能保持優(yōu)異的力學性能依賴于其特殊顯微結(jié)構(gòu)。鎳基單晶高溫合金顯微結(jié)構(gòu)由γ相中彌散分布大量γ'相構(gòu)成。為提高合金高溫服役的穩(wěn)定性,合金中加入了十種以上合金強化元素。添加的合金元素對合金的相結(jié)構(gòu)、缺陷結(jié)構(gòu)的作用直接決定合金的高溫性能。研究各個合金元素的強化機理,給出具有最佳服役性能時的微觀相結(jié)構(gòu)和缺陷結(jié)構(gòu),確定最佳熔煉工藝、加工工藝、熱處理工藝,是得到優(yōu)質(zhì)單晶鎳基高溫合金的主要途徑。本論文利用原位電子顯微學、原位X射線衍射等測試分析技術(shù),對鎳基單晶高溫合金DD5在近服役條件下的高溫氧化、高溫時效、相界面遷移、重要合金元素與缺陷的交互作用、顯微結(jié)構(gòu)演化與合金的性能進行了研究,具體研究內(nèi)容如下:(1)原位研究鎳基單晶高溫合金高溫低壓氧化過程:在環(huán)境透射電子顯微鏡(TEM)中利用加熱樣品臺原位測試研究鎳基單晶高溫合金DD5在850℃、氧壓5*10-2Pa條件下,兩相氧化過程和氧化誘導的γ'相轉(zhuǎn)變?yōu)棣孟噙^程。高分辨TEM、選區(qū)電子衍射(SAED)、X射線能量色散譜(EDS)、電子能量損失譜(EELS)等測試分析研究表明γ'相低壓氧化產(chǎn)物為尺寸約1～3nm、取向與原 γ'相共格的γ-Al_2O_3納米晶,與原有相共格關(guān)系為(111)γ-Al_2O_3//(001)γ',[1(?)0]γ-Al_2O_3//[1(?)0]γ'或[110]γ-Al_2O_3//[(?)(?)0]γ;γ相低壓氧化產(chǎn)物主要為疏松NiO納米顆粒。從納米尺度上證明:氧化過程中γ'相有序結(jié)構(gòu)隨著γ-Al_2O_3的產(chǎn)生被逐漸破壞,即γ'相中的A1元素被氧化導致γ'-Y相變。同時分析研究證明了高溫合金中氧優(yōu)先擴散通道為Y/Y'相界面。(2)實現(xiàn)了對時效過程中的鎳基單晶高溫合金晶體結(jié)構(gòu)演變的表征。通過原位高溫X射線衍射(XRD)試驗發(fā)現(xiàn),隨溫度升高γ與γγ相晶格常數(shù)迅速升高,錯配度絕對值逐漸減小;在保溫時效過程中,隨著時效時間的延長,合金中溶質(zhì)元素發(fā)生再分配會導致γ與γ'相晶格常數(shù)略微增加,但合金中γ/γ,相界面的錯配度基本無變化。(3)發(fā)展了一種新型制備塊體材料原位芯片加熱TEM樣品的方法:在聚焦離子束加工儀(FIB)中將TEM樣品中適合觀察的區(qū)域轉(zhuǎn)移至加熱芯片上,保證了原位觀察樣品薄區(qū)大、鎵離子污染較少且變溫過程中較穩(wěn)定。對于需要預先甄選樣品形貌的原位試驗,該方法可大大縮短制樣周期。該方法也適用于其他導電塊體材料。(4)原位研究相界面與相界面位錯在相界面遷移過程中的交互作用:利用原位加熱樣品臺在球差校正電鏡中,直接測試分析溫度變化時γ/γ'相界面的遷移行為,證明了相界面遷移會導致相界面位錯發(fā)生位置和形態(tài)的改變,但位錯始終位于界面上不會逃逸;相界面與單根界面位錯的交互作用產(chǎn)生的相界面凹槽為尖角狀,表明位錯對相界面的影響范圍較窄;結(jié)合位錯核成分分析,本文提出一種新型相界面凹槽形成機制,界面位錯附近偏聚的錸元素能夠有效阻礙γ相中的γ'相形成元素Ni和A1擴散至γ'相,阻礙相界面遷移,進而在相界面附近形成凹槽。(5)關(guān)鍵合金元素錸在鎳基單晶高溫合金DD5界面位錯網(wǎng)絡成分分布:結(jié)合高分辨掃描透射電子顯微像(STEM)和Super-X對界面位錯核心成分進行定量測試分析,確定錸元素偏聚于位錯核心;發(fā)現(xiàn)熱處理條件可調(diào)控鎳基單晶高溫合金相界面位錯核心錸偏聚的濃度:a)冷卻速度越慢,錸濃度越高;b)時效時長對界面位錯核錸濃度分布區(qū)間影響不大,但會降低位錯核之間錸濃度差別,即界面位錯核錸分布更均勻;c)高溫時效后先緩冷后回爐能夠大大縮短將相界面位錯核錸濃度提升至一定數(shù)值所需時間。(6)原位研究了錸元素偏聚于界面位錯核對鎳基單晶高溫合金性能的影響:在TEM中利用原位力學樣品臺研究了相界面位錯核心錸濃度不同的樣品中位錯的行為,發(fā)現(xiàn)錸偏聚于界面位錯核能夠顯著強化γ/γ'相界面。位錯核低錸的相界面對位錯運動阻礙作用較弱,位錯易剪切相界面;而位錯核高錸的相界面對位錯運動的阻礙作用顯著,位錯運動局限于γ相內(nèi),剪切相界面較難。分子動力學和Monte Carrlo模擬計算研究表明錸偏聚對位錯結(jié)構(gòu)影響較小,能大幅降低界面位錯能量(加入30wt.%錸后,位錯每納米長度能量下降152.7eV),穩(wěn)定界面位錯網(wǎng)絡,并使位錯附近彈性應力場復雜化,影響運動位錯行為。本文對鎳基單晶高溫合金DD5高溫氧化、高溫時效、相界面遷移、錸與界面位錯交互作用的研究,可為進一步研究高溫服役時合金顯微組織演變和強化機理提供試驗依據(jù),為優(yōu)化合金微觀結(jié)構(gòu)、熱處理工藝、優(yōu)化合金成分、提高合金性能提供路線途徑。
[Abstract]:Nickel based single crystal superalloy is the preferred structural material widely used in aero engine turbine blades. Its working characteristics are high temperature and high stress environment. The alloy still maintains excellent mechanical properties at high temperature and depends on its special microstructure. The microstructure of the nickel base single crystal superalloy is composed of a large amount of gamma phase dispersed in the gamma phase. In order to improve the stability of high temperature service of the alloy, more than ten alloying elements are added in the alloy. The effect of alloying elements on the phase structure and defect structure of the alloy determines the high temperature properties of the alloy directly. The strengthening mechanism of the alloying elements is studied, and the microstructure and defect structure with the best service properties are given. The main way to obtain high quality single crystal nickel base superalloy is to determine the best melting process, processing technology and heat treatment process. In this paper, in situ electron microscopy, in situ X ray diffraction and other testing and analysis techniques, the high temperature oxidation, high temperature aging, phase interface migration and important alloy elements of nickel base single crystal superalloy DD5 under the near service condition The interaction of the defects and the microstructure evolution and the properties of the alloys are studied. The specific research contents are as follows: (1) the in situ study of the high temperature and low temperature oxidation process of nickel base single crystal superalloy at high temperature and low pressure: in the environment transmission electron microscope (TEM), the nickel base single crystal superalloy DD5 was studied by the heating sample table in situ, and the oxygen pressure 5*10-2Pa strip was studied at the temperature of the nickel base single crystal superalloy. The two phase oxidation process and the oxidation induced gamma phase transition to gamma phase process. High resolution TEM, selective electron diffraction (SAED), X ray energy dispersive spectrum (EDS), electron energy loss spectrum (EELS) and other tests show that gamma phase low pressure oxidation product is a gamma -Al_2O_3 nanocrystalline with a size of about 1 to 3nm, and a common lattice of the original gamma phase. The lattice relation is (111) gamma -Al_2O_3// (001) gamma ', [1 (?) 0] gamma -Al_2O_3//[1 (?) 0] gamma or [110] gamma -Al_2O_3//[(?) 0] gamma; the low-pressure oxidation products of the gamma phase are mainly loose NiO nanoparticles. It is proved from the nanoscale that the ordered structure of gamma phase in the oxidation process is gradually destroyed with the production of gamma -Al_2O_3, that is, the A1 element in the gamma phase is oxidized to gamma'-Y phase. The study shows that the oxygen preferential diffusion channel in the superalloy is Y/Y'phase interface. (2) the crystal structure evolution of the nickel base single crystal superalloy in the aging process is characterized. The lattice constant of the gamma and gamma phase increases rapidly with the temperature rising, and the absolute value of the mismatch degree decreases gradually. In the process of aging and aging, with the prolongation of aging time, the redistribution of the solute elements in the alloy leads to a slight increase in the lattice constant of gamma and gamma, but the mismatch degree of the phase interface in the alloy is basically unchanged. (3) a new method of heating TEM samples by a new type of block material in situ chip is developed: in the focusing ion beam processing instrument (FIB) the area of the suitable observation in the TEM sample is transferred to the heating chip to ensure that the in situ observation sample thin area is large, the gallium ion pollution is less and the temperature changing process is more stable. In situ test for the selection of sample morphology in advance, this method can greatly shorten the sample preparation period. This method is also suitable for other conductive block materials. (4) in situ The interaction of phase interface and phase interface dislocation in the process of phase interface migration is studied. Using in situ heating sample table in spherical aberration mirror, the migration behavior of gamma / gamma interface is directly measured and analyzed. It is proved that phase interface migration will lead to dislocation position and shape change of phase interface dislocation, but the dislocation is always located in the interface. There is no escape, and the interphase interface with the single interface dislocation has a sharp angle, indicating that the dislocation has a narrow influence on the phase interface. In combination with the analysis of the dislocation nuclei, a new type of phase interface groove formation mechanism is proposed, and the rhenium in the vicinity of the interface dislocation can effectively impede the gamma phase in the gamma phase. The elements Ni and A1 diffuse to the gamma 'phase, obstruct the migration of the phase interface, and then form a groove near the phase interface. (5) the key alloying element rhenium is distributed in the interface dislocation network of the nickel base single crystal superalloy DD5 interface: the quantitative test and analysis of the core components of the boundary dislocation with the high-resolution scanning transmission electron microscope (STEM) and Super-X are used to determine the rhenium. It is found that the heat treatment conditions can regulate the concentration of rhenium at the core of the interface dislocation at the interface of the nickel base single crystal superalloy: a) the slower the cooling rate, the higher the rhenium concentration, and the time of B), which have little influence on the distribution of the rhenium concentration in the dislocation nuclei, but it will reduce the rhenium concentration difference between the dislocation nuclei, that is, the distribution of the rhenium in the interface dislocation nuclei is more uniform. C) the time required to improve the concentration of the dislocation nuclear rhenium to a certain value after the first slow cooling after high temperature aging. (6) the effect of the rhenium element on the properties of the nickel based single crystal superalloy at the interface dislocation nucleation was investigated in situ: in the TEM, the concentration of rhenium at the core of the phase dislocation in the phase interface is different. The behavior of dislocation in the sample shows that rhenium segregation at the dislocation nucleus can significantly strengthen the interface of gamma / gamma phase. The phase boundary of the dislocations is weak and the dislocation is easy to shear phase interface, while the phase boundary of the high rhenium in the dislocation nucleus is significantly hindered by the dislocation motion, and the dislocation movement is confined to the gamma phase, and the shear phase interface is difficult. The study of molecular dynamics and Monte Carrlo simulation shows that rhenium segregation has little influence on dislocation structure, and can greatly reduce the interface dislocation energy (after adding 30wt.% rhenium, the dislocation per nanometer energy drop 152.7eV), stabilize the interface dislocation network, and compound the elastic stress field near the dislocation, and affect the motion dislocation behavior. The study of high temperature oxidation, high temperature aging, phase interface migration and the interaction of rhenium with interface dislocation can provide experimental basis for further research on microstructure evolution and strengthening mechanism of alloy at high temperature service, and provide a route for optimizing alloy microstructure, heat treatment process, optimizing alloy composition and improving alloy properties DD5.
【學位授予單位】：浙江大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TG132.3
本文編號：2140417
[Abstract]:Nickel based single crystal superalloy is the preferred structural material widely used in aero engine turbine blades. Its working characteristics are high temperature and high stress environment. The alloy still maintains excellent mechanical properties at high temperature and depends on its special microstructure. The microstructure of the nickel base single crystal superalloy is composed of a large amount of gamma phase dispersed in the gamma phase. In order to improve the stability of high temperature service of the alloy, more than ten alloying elements are added in the alloy. The effect of alloying elements on the phase structure and defect structure of the alloy determines the high temperature properties of the alloy directly. The strengthening mechanism of the alloying elements is studied, and the microstructure and defect structure with the best service properties are given. The main way to obtain high quality single crystal nickel base superalloy is to determine the best melting process, processing technology and heat treatment process. In this paper, in situ electron microscopy, in situ X ray diffraction and other testing and analysis techniques, the high temperature oxidation, high temperature aging, phase interface migration and important alloy elements of nickel base single crystal superalloy DD5 under the near service condition The interaction of the defects and the microstructure evolution and the properties of the alloys are studied. The specific research contents are as follows: (1) the in situ study of the high temperature and low temperature oxidation process of nickel base single crystal superalloy at high temperature and low pressure: in the environment transmission electron microscope (TEM), the nickel base single crystal superalloy DD5 was studied by the heating sample table in situ, and the oxygen pressure 5*10-2Pa strip was studied at the temperature of the nickel base single crystal superalloy. The two phase oxidation process and the oxidation induced gamma phase transition to gamma phase process. High resolution TEM, selective electron diffraction (SAED), X ray energy dispersive spectrum (EDS), electron energy loss spectrum (EELS) and other tests show that gamma phase low pressure oxidation product is a gamma -Al_2O_3 nanocrystalline with a size of about 1 to 3nm, and a common lattice of the original gamma phase. The lattice relation is (111) gamma -Al_2O_3// (001) gamma ', [1 (?) 0] gamma -Al_2O_3//[1 (?) 0] gamma or [110] gamma -Al_2O_3//[(?) 0] gamma; the low-pressure oxidation products of the gamma phase are mainly loose NiO nanoparticles. It is proved from the nanoscale that the ordered structure of gamma phase in the oxidation process is gradually destroyed with the production of gamma -Al_2O_3, that is, the A1 element in the gamma phase is oxidized to gamma'-Y phase. The study shows that the oxygen preferential diffusion channel in the superalloy is Y/Y'phase interface. (2) the crystal structure evolution of the nickel base single crystal superalloy in the aging process is characterized. The lattice constant of the gamma and gamma phase increases rapidly with the temperature rising, and the absolute value of the mismatch degree decreases gradually. In the process of aging and aging, with the prolongation of aging time, the redistribution of the solute elements in the alloy leads to a slight increase in the lattice constant of gamma and gamma, but the mismatch degree of the phase interface in the alloy is basically unchanged. (3) a new method of heating TEM samples by a new type of block material in situ chip is developed: in the focusing ion beam processing instrument (FIB) the area of the suitable observation in the TEM sample is transferred to the heating chip to ensure that the in situ observation sample thin area is large, the gallium ion pollution is less and the temperature changing process is more stable. In situ test for the selection of sample morphology in advance, this method can greatly shorten the sample preparation period. This method is also suitable for other conductive block materials. (4) in situ The interaction of phase interface and phase interface dislocation in the process of phase interface migration is studied. Using in situ heating sample table in spherical aberration mirror, the migration behavior of gamma / gamma interface is directly measured and analyzed. It is proved that phase interface migration will lead to dislocation position and shape change of phase interface dislocation, but the dislocation is always located in the interface. There is no escape, and the interphase interface with the single interface dislocation has a sharp angle, indicating that the dislocation has a narrow influence on the phase interface. In combination with the analysis of the dislocation nuclei, a new type of phase interface groove formation mechanism is proposed, and the rhenium in the vicinity of the interface dislocation can effectively impede the gamma phase in the gamma phase. The elements Ni and A1 diffuse to the gamma 'phase, obstruct the migration of the phase interface, and then form a groove near the phase interface. (5) the key alloying element rhenium is distributed in the interface dislocation network of the nickel base single crystal superalloy DD5 interface: the quantitative test and analysis of the core components of the boundary dislocation with the high-resolution scanning transmission electron microscope (STEM) and Super-X are used to determine the rhenium. It is found that the heat treatment conditions can regulate the concentration of rhenium at the core of the interface dislocation at the interface of the nickel base single crystal superalloy: a) the slower the cooling rate, the higher the rhenium concentration, and the time of B), which have little influence on the distribution of the rhenium concentration in the dislocation nuclei, but it will reduce the rhenium concentration difference between the dislocation nuclei, that is, the distribution of the rhenium in the interface dislocation nuclei is more uniform. C) the time required to improve the concentration of the dislocation nuclear rhenium to a certain value after the first slow cooling after high temperature aging. (6) the effect of the rhenium element on the properties of the nickel based single crystal superalloy at the interface dislocation nucleation was investigated in situ: in the TEM, the concentration of rhenium at the core of the phase dislocation in the phase interface is different. The behavior of dislocation in the sample shows that rhenium segregation at the dislocation nucleus can significantly strengthen the interface of gamma / gamma phase. The phase boundary of the dislocations is weak and the dislocation is easy to shear phase interface, while the phase boundary of the high rhenium in the dislocation nucleus is significantly hindered by the dislocation motion, and the dislocation movement is confined to the gamma phase, and the shear phase interface is difficult. The study of molecular dynamics and Monte Carrlo simulation shows that rhenium segregation has little influence on dislocation structure, and can greatly reduce the interface dislocation energy (after adding 30wt.% rhenium, the dislocation per nanometer energy drop 152.7eV), stabilize the interface dislocation network, and compound the elastic stress field near the dislocation, and affect the motion dislocation behavior. The study of high temperature oxidation, high temperature aging, phase interface migration and the interaction of rhenium with interface dislocation can provide experimental basis for further research on microstructure evolution and strengthening mechanism of alloy at high temperature service, and provide a route for optimizing alloy microstructure, heat treatment process, optimizing alloy composition and improving alloy properties DD5.
【學位授予單位】：浙江大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TG132.3
【參考文獻】
相關(guān)期刊論文 前3條
1 ;Measurements of γ/γ' Lattice Misfit and γ' Volume Fraction for a Ru-containing Nickel-based Single Crystal Superalloy[J];Journal of Materials Science & Technology;2011年10期
2 駱宇時;劉世忠;孫鳳禮;;錸在單晶高溫合金中強化機理的研究現(xiàn)狀[J];材料導報;2005年08期
3 ;Effects of Rhenium on Creep Rupture Life of a Single Crystal Superalloys[J];Journal of Materials Science & Technology;1999年01期
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